White Mountains Insurance Group, Ltd.
| Security | WTM / White Mountains Insurance Group, Ltd. |
| Institution | Janus Henderson Group Plc |
| Latest Disclosed Ownership | 1,123 shares |
| Latest Disclosed Value | $ 2,461,919 |
Janus Henderson Group Plc ownership in WTM / White Mountains Insurance Group, Ltd.
On May 18, 2026 - Janus Henderson Group Plc filed a 13F-HR/A form disclosing ownership of 1,123 shares of White Mountains Insurance Group, Ltd. (US:WTM) valued at $2,467,186 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 1,123 shares of White Mountains Insurance Group, Ltd.. This represents a change in shares of 0.00% during the quarter. The current value of the position is $2,263,451 USD.
Institutional Ownership: 13F and NPORT Filings
The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.
Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.
Upgrade
to unlock premium data and export to Excel 
.
Disclosed Equity Positions (from 13F/NPORT Filings)
| File Date |
Effective Date | Form | Security | Class | ID | Avg Price Paid (Est) |
Reported Shares |
ΔShares | ΔShares (%) |
Reported Value (x1000) |
ΔValue (%) |
Alloc (%) |
ΔAlloc | ΔAlloc (%) | Cost Basis (x1000) |
Unrealized Gain/Loss (x1000) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2026-05-18 | 2026-03-31 | 13F/A-1 | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | 0 | 0.00 | 2,462 | 5.40 | 0.0004 | |||||
| 2026-05-15 | 2026-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | 0 | 2,462 | 0.0005 | |||||||
| 2026-02-17 | 2025-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | 0 | 0.00 | 2,336 | 24.40 | 0.0010 | |||||
| 2025-11-14 | 2025-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | 0 | 0.00 | 1,878 | -6.66 | 0.0009 | |||||
| 2025-08-14 | 2025-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | 0 | 0.00 | 2,011 | -6.03 | 0.0010 | |||||
| 2025-05-15 | 2025-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | -1,293 | -53.52 | 2,141 | -54.48 | 0.0012 | |||||
| 2025-02-14 | 2024-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,416 | 1,193 | 97.55 | 4,702 | 127.10 | 0.0024 | |||||
| 2024-11-14 | 2024-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,223 | 0 | 0.00 | 2,071 | -7.30 | 0.0011 | |||||
| 2024-08-14 | 2024-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,223 | -12 | -0.97 | 2,233 | 0.09 | 0.0012 | |||||
| 2024-05-15 | 2024-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,235 | 0 | 0.00 | 2,232 | 19.37 | 0.0012 | |||||
| 2024-02-14 | 2023-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,235 | -3 | -0.24 | 1,869 | 0.59 | 0.0011 | |||||
| 2023-11-14 | 2023-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,238 | 0 | 0.00 | 1,858 | 8.02 | 0.0012 | |||||
| 2023-08-14 | 2023-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,238 | -1 | -0.08 | 1,721 | 1.00 | 0.0011 | |||||
| 2023-05-15 | 2023-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,239 | 711 | 134.66 | 1,704 | 128.59 | 0.0011 | |||||
| 2023-02-14 | 2022-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 528 | 1 | 0.19 | 745 | 8.44 | 0.0005 | |||||
| 2022-11-14 | 2022-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 527 | -99 | -15.81 | 687 | -12.04 | 0.0005 | |||||
| 2022-08-15 | 2022-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 626 | -2 | -0.32 | 781 | 9.08 | 0.0005 | |||||
| 2022-05-16 | 2022-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 628 | 0 | 0.00 | 716 | 12.23 | 0.0003 | |||||
| 2022-02-14 | 2021-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 628 | 316 | 101.28 | 638 | 91.02 | 0.0003 | |||||
| 2021-11-16 | 2021-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 312 | 312 | 334 | 0.0001 | |||||||
| 2020-11-16 | 2020-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 0 | -620 | -100.00 | 0 | -100.00 | ||||||
| 2020-08-14 | 2020-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 620 | -503 | -44.79 | 551 | -46.09 | 0.0003 | |||||
| 2020-05-14 | 2020-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,123 | -1,418 | -55.80 | 1,022 | -63.95 | 0.0007 | |||||
| 2020-02-18 | 2019-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,541 | -136 | -5.08 | 2,835 | -1.94 | 0.0015 | |||||
| 2019-11-14 | 2019-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,677 | 1,274 | 90.81 | 2,891 | 101.74 | 0.0016 | |||||
| 2019-07-31 | 2019-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,403 | -1,035 | -42.45 | 1,433 | -36.48 | 0.0008 | |||||
| 2019-04-30 | 2019-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,438 | 0 | 0.00 | 2,256 | 7.89 | 0.0013 | |||||
| 2019-02-06 | 2018-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,438 | 238 | 10.82 | 2,091 | 1.55 | 0.0013 | |||||
| 2018-11-09 | 2018-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 2,200 | 1,300 | 144.44 | 2,059 | 152.33 | 0.0011 | |||||
| 2018-08-10 | 2018-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 900 | -100 | -10.00 | 816 | -0.85 | 0.0005 | |||||
| 2018-05-14 | 2018-03-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,000 | -200 | -16.67 | 823 | -19.47 | 0.0005 | |||||
| 2018-03-12 | 2017-12-31 | 13F/A-1 | WHITE MTNS INS GROUP | COM | G9618E107 | 1,200 | -4,400 | -78.57 | 1,022 | -78.70 | 0.0006 | |||||
| 2018-02-09 | 2017-12-31 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 1,200 | -4,400 | 1,022 | ||||||||
| 2017-11-14 | 2017-09-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 5,600 | -6,500 | -53.72 | 4,799 | -54.34 | 0.0031 | |||||
| 2017-08-17 | 2017-06-30 | 13F/A-1 | WHITE MTNS INS GROUP | COM | G9618E107 | 12,100 | 12,100 | 10,510 | 0.0072 | |||||||
| 2017-08-14 | 2017-06-30 | 13F | WHITE MTNS INS GROUP | COM | G9618E107 | 12,100 | 10,510 |
Legend
- Shares
- The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
- Value
- The total value of the shares as of the effective date. This is provided in the filing.
- Avg. Share Price
- The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
- Class
- This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
- Allocation (%)
- The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
- Change in Allocation
- The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
- Change in Allocation (%)
- The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
- Cost Basis
- The total cost of the shares held. This is calculated as reported shares * avg. share price
- Unrealized Gain/Loss
- This is the market value of the position as of the effective date minus the cost basis.
